Foreword

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This document was prepared by Technical Committee ISO/TC 85, Nuclear Energy, nuclear technologies, and radiological protection, Subcommittee SC 6, Reactor technology. This document is based on a standard developed by the American Nuclear Society (ANS) of which the current version is ANSI/ANS-19.3-2022^[2^].

This second edition cancels and replaces the first (ISO 18075:2018), which has been technically revised.

The main changes are as follows:

addition of new terms in Clause 3;
figures slightly revised;
5.8.5 was amended so that CANDU is only an example;
correction of internal references;
Table A.1 corrected;
editorial amendments in the whole document.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

The design and operation of nuclear reactors require knowledge of the conditions under which a reactor will be critical, as well as the degree of subcriticality or supercriticality when these conditions change. In addition, knowledge is required of the spatial distribution of neutron reaction rates in reactor components as a prerequisite, for example, for inferring proper power and temperature distributions to ensure the satisfaction of thermal-limit and safety-limit requirements. Both reaction-rate spatial distributions and reactivity have been measured by suitable experimental techniques, either in mock-ups or in the operating reactors themselves. These quantities can also be calculated by various techniques. Available reactor experimental data have been used to validate the steady-state neutronic calculations within reasonable margins. As more accurate nuclear cross sections and improved calculation methods have become available, steady-state neutronic calculations have been utilized extensively for nuclear fuel and core designs and analyses and thus have become increasingly important.

1 Scope

This document provides guidance for performing and validating the sequence of steady-state calculations leading to prediction in all types of operating commercial nuclear reactors, of the following:

reaction-rate spatial distributions;
reactivity;
change of nuclide compositions with time.

The document provides

guidance for the selection of computational methods,
criteria for verification and validation of calculation methods used by reactor core analysts,
criteria for evaluation of accuracy and range of applicability of data and methods, and
requirements for documentation of the preceding.

2 Normative references

3 Terms, definitions and abbreviations

3.1 Terms and definitions

3.2 Abbreviations

4 Relation to other standards

5 Methods of calculation

5.1 General

5.2 Conditions to be considered

5.3 Multigroup cross sections

5.4 Collapse to few-groups and spatial homogenization

5.5 Calculation of reactivity, reaction rates and neutron flux distributions

5.6 Calculation of reaction rates in reactor components

5.7 Depletion calculations

5.8 Common practices

6 Verification and validation of the calculation system

6.1 Overview

6.2 Verification

6.3 Validation

6.4 Biases and uncertainties

7 Documentation

8 Summary of requirements

Bibliography